The liberation and metabolism of arachidonic acid (AA) from the cell membrane, results in the generation of pro-inflammatory metabolites by several different pathways. Arguably, two of the most important pathways to inflammation are mediated by the enzymes 5-lipoxygenase (5-LO) and cyclooxygenase (COX). These are parallel pathways that result in the generation of leukotrienes and prostaglandins, respectively, which play important roles in the initiation and progression of the inflammatory response. These vasoactive compounds are chemotaxins, which both promote infiltration of inflammatory cells into tissues and serve to prolong the inflammatory response. Consequently, the enzymes responsible for generating these mediators of inflammation have become the targets for many new drugs aimed at the treatment of inflammation, which that contributes to the pathogenesis of diseases such as rheumatoid arthritis, osteoarthritis, Alzheimer's disease and certain types of cancer.
Inhibition of the enzyme cyclooxygenase (COX) is the mechanism of action attributed to most nonsteroidal anti-inflammatory drugs (NSAIDS). There are two distinct isoforms of the COX enzyme (COX-1 and COX-2) that share approximately 60% sequence homology, but differ in expression profiles and function. COX-1 is a constitutive form of the enzyme that has been linked to the production of physiologically important prostaglandins, which help regulate normal physiological functions, such as platelet aggregation, protection of cell function in the stomach and maintenance of normal kidney function. (Dannhardt and Kiefer (2001) Eur. J. Med. Chem. 36:109-26). The second isoform, COX-2, is a form of the enzyme that is inducible by pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and other growth factors. (Herschmann (1994) Cancer Metastasis Rev. 134:241-56; Xie et al. (1992) Drugs Dev. Res. 25:249-65). This isoform catalyzes the production of prostaglandin E2 (PGE2) from arachidonic acid (AA). Inhibition of COX-2 is responsible for the anti-inflammatory activities of conventional NSAIDs.
Inhibitors that demonstrate dual specificity for COX-2 and 5-LO while maintaining COX-2 selectivity relative to COX-1 would have the obvious benefit of inhibiting multiple pathways of arachidonic acid metabolism. Such inhibitors would block the inflammatory effects of PGE2, as well as, those of multiple leukotrienes (LT) by limiting their production. This includes the vasodilation, vasopermeability and chemotactic effects of LTB4 and LTD4 and the effects of LTE4, also known as the slow reacting substance of anaphalaxis. Of these, LTB4 has the most potent chemotactic and chemokinetic effects (Moore (1985) Prostanoids: phaenacological, physiological and clinical relevance. Cambridge University Press, N.Y., pp. 229-30) and has been shown to be elevated in the gastrointestinal mucosa of patients with inflammatory bowel disease (Sharon and Stenson (1983) Gastroenterology 84:1306-13) and within the synovial fluid of patients with rheumatoid arthritis. (Klicksein et al. (1980) J. Clin. Invest. 66:1166-70; Rae et al. (1982) Lancet ii:1122-4).
In addition to the above-mentioned benefits of dual COX-2/5-LO inhibitors, many dual inhibitors do not cause some of the side effects that are typical of NSAIDs or COX-2 inhibitors, including both the gastrointestinal damage and discomfort caused by traditional NSAIDs. It has been suggested that NSAID induced gastric inflammation is largely due to metabolites of 5-LO, particularly LTB4. (Kircher et al. (1997) Prostaglandins leukotrienes and essential fatty acids 56:417-23). Leukotrienes represent the primary arachidonic acid metabolites within the gastric mucosa following prostanoid inhibition. It appears that these compounds contribute to a significant amount of the gastric epithelial injury resulting from the use of NSAIDs. (Celotti and Laufer (2001) Pharmacological Research 43:429-36). Dual inhibitors of COX and 5-LO were also demonstrated to inhibit the coronary vasoconstriction in arthritic hearts in a rat model. (Gok et al. (2000) Pharmacology 60:41-46). Taken together, these characteristics suggest that there may be distinct advantages to dual inhibitors of COX-2 and 5-LO over COX-2 inhibitors and NSAIDs alone with regard to both increased efficacy and a lack of side effects.
Because the mechanism of action of COX inhibitors overlaps that of most conventional NSAID's, COX inhibitors are used to treat many of the same symptoms, including pain and swelling associated with inflammation in transient conditions and chronic diseases in which inflammation plays a critical role. Transient conditions include treatment of inflammation associated with minor abrasions, sunburn or contact dermatitis, as well as, the relief of pain associated with tension and migraine headaches and menstrual cramps. Applications to chronic conditions include arthritic diseases, such as rheumatoid arthritis and osteoarthritis. Although, rheumatoid arthritis is largely an autoimmune disease and osteoarthritis is caused by the degradation of cartilage in joints, reducing the inflammation associated with each provides a significant increase in the quality of life for those suffering from these diseases. (Wienberg (2001) Immunol. Res. 22:319-41; Wollhiem (2000) Curr. Opin. Rheum. 13:193-201). In addition to rheumatoid arthritis, inflammation is a component of rheumatic diseases in general. Therefore, the use of COX inhibitors has been expanded to include diseases, such as systemic lupus erythromatosus (SLE) (Goebel et al. (1999) Chem. Res. Tox. 12:488-500; Patrono et al. (1985) J. Clin. Invest. 76:1011-1018), as well as, rheumatic skin conditions, such as scleroderma. COX inhibitors are also used for the relief of inflammatory skin conditions that are not of rheumatic origin, such as psoriasis, in which reducing the inflammation resulting from the over production of prostaglandins could provide a direct benefit. (Fogh et al. (1993) Acta Derm Venerologica 73:191-3). Simply stated COX inhibitors are useful for the treatment of symptoms of chronic inflammatory diseases, as well as, the occasional ache and pain resulting from transient inflammation.
In addition to their use as anti-inflammatory agents, another potential role for COX inhibitors is in the treatment of cancer. Over expression of COX-2 has been demonstrated in various human malignancies and inhibitors of COX-2 have been shown to be efficacious in the treatment of animals with skin, breast and bladder tumors. While the mechanism of action is not completely understood, the over expression of COX-2 has been shown to inhibit apoptosis and increase the invasiveness of tumorgenic cell types. (Dempke et al. (2001) J. Can. Res. Clin. Oncol. 127:411-17; Moore and Simmons (2000) Current Med. Chem. 7:1131-44). It is possible that enhanced production of prostaglandins resulting from the over expression of COX-2 promotes cellular proliferation and consequently, increases angiogenesis. (Moore (1985) in Prostanoids: pharmacological, physiological and clinical relevance, Cambridge University Press, N.Y., pp. 229-30; Fenton et al. (2001) Am. J. Clin. Oncol. 24:453-57).
There have been a number of clinical studies evaluating COX-2 inhibitors for potential use in the prevention and treatment of different types of cancer. In 1999, 130,000 new cases of colorectal cancer were diagnosed in the U.S. Aspirin, a non-specific NSAID, for example, has been found to reduce the incidence of colorectal cancer by 40-50% (Giovannucci et al. (1995) N Engl J. Med. 333:609-614) and mortality by 50% (Smalley et al. (1999) Arch Intern Med. 159:161-166). In 1999, the FDA approved the COX-2 inhibitor CeleCOXib for use in FAP (Familial Ademonatous Polyposis) to reduce colorectal cancer mortality. It is believed that other cancers, with evidence of COX-2 involvement, may be successfully prevented and/or treated with COX-2 inhibitors including, but not limited to esophageal cancer, head and neck cancer, breast cancer, bladder cancer, cervical cancer, prostate cancer, hepatocellular carcinoma and non-small cell lung cancer. (Jaeckel et al. (2001) Arch. Otolarnygol. 127:1253-59; Kirschenbaum et al. (2001) Urology 58:127-31; Dannhardt and Kiefer (2001) Eur. J. Med. Chem. 36:109-26). COX-2 inhibitors may also prove successful in preventing colon cancer in high-risk patients. There is also evidence that COX-2 inhibitors can prevent or even reverse several types of life-threatening cancers. To date, as many as fifty studies show that COX-2 inhibitors can prevent premalignant and malignant tumors in animals, and possibly prevent bladder, esophageal and skin cancers as well. COX-2 inhibition could prove to be one of the most important preventive medical accomplishments of the century.
Recent scientific progress has identified correlations between COX-2 expression, general inflammation and the pathogenesis of Alzheimer's disease (AD). (Ho et al. (2001) Arch. Neurol. 58:487-92). In animal models, transgenic mice that over express the COX-2 enzyme have neurons that are more susceptible to damage. The National Institute on Aging (NIA) is launching a clinical trial to determine whether NSAIDs can slow the progression of Alzheimer's disease. Naproxen (a non-selective NSAID) and rofecoxib (Vioxx, a COX-2 specific selective NSAID) will be evaluated. Previous evidence has indicated inflammation contributes to Alzheimer's disease. According to the Alzheimer's Association and the NIA, about 4 million people suffer from AD in the U.S.; and this is expected to increase to 14 million by mid-century.
The COX enzyme (also known as prostaglandin H2 synthase) catalyzes two separate reactions. In the first reaction, arachidonic acid is metabolized to form the unstable prostaglandin G2 (PGG2), a cyclooxygenase reaction. In the second reaction, PGG2 is converted to the endoperoxide PGH2, a peroxidase reaction. The short-lived PGH2 non-enzymatically degrades to PGE2. The compounds described herein are the result of a discovery strategy that combined an assay focused on the inhibition of COX-1 and COX-2 peroxidase activity with a chemical dereplication process to identify novel inhibitors of the COX enzymes.
Acacia is a genus of leguminous trees and shrubs. The genus Acacia includes more than 1000 species belonging to the family of Leguminosae and the subfamily of Mimosoideae. Acacias are distributed worldwide in tropical and subtropical areas of central and south America, Africa, parts of Asia, as well as, Australia, which has the largest number of endemic species. Acacias occur primarily in dry and arid regions, where the forests are often in the nature of open thorny shrubs. The genus Acacia is divided into 3 subgenera based mainly on the leaf morphology—Acacia, Aculiferum and Heterophyllum. Based on the nature of the leaves of mature trees, however, the genus Acacia can be divided into two “popular” groups: the typical bipinnate leaved species and the phyllodenous species. A phyllode is a modified petiole expanded into a leaflike structure with no leaflets, an adaptation to xerophytic conditions. The typical bipinnate leaved species are found primarily throughout the tropics, whereas the phyllodenous species occur mainly in Australia. More than 40 species of Acacia have been reported in India. Gamble in his Flora of Madras Presidency listed 23 native species for southern India, 15 of which are found in Tamil Nadu. Since that time, many new Acacia species have been introduced to India. Approximately 40 species are now found in Tamil Nadu itself. The indigenous species are primarily thorny trees or shrubs and a few are thorny stragglers, such as A. caesia, A. pennata and A. sinuata. Many species have been introduced from Africa and Australia, i.e. Acacia meamsii, A. picnantha and A. dealbata, which have bipinnate leaves and A. auriculiformis, A. holoserecia and A. mangium, which are phyllodenous species.
Acacias are very important economically, providing a source of tannins, gums, timber, fuel and fodder. Tannins, which are isolated primarily from bark, are used extensively for tanning hides and skins. Some Acacia barks are also used for flavoring local spirits. Some indigenous species like A. sinuata also yield saponins, which are any of various plant glucosides that form soapy lathers when mixed and agitated with water. Saponins are used in detergents, foaming agents and emulsifiers. The flowers of some Acacia species are fragrant and used to make perfume. For example, Cassie perfume is obtained from Acacia ferrugenea. The heartwood of many Acacias is used for making agricultural implements and also provides a source of firewood. Acacia gums find extensive use in medicine and confectionary and as sizing and finishing materials in the textile industry. Lac insects can be grown on several species, including A. nilotica and A. catechu. Some species have been used for forestation of wastelands, including A. nilotica, which can withstand some water inundation and a few such areas have become bird sanctuaries.
To date, approximately 330 compounds have been isolated from various Acacia species. Flavonoids, a type of water-soluble plant pigments, are the major class of compounds isolated from Acacias. Approximately 180 different flavonoids have been identified, 111 of which are flavans. Terpenoids are second largest class of compounds isolated from species of the Acacia genus, with 48 compounds having been identified. Other classes of compounds isolated from Acacia include, alkaloids (28), amino acids/peptides (20), tannins (16), carbohydrates (15), oxygen heterocycles (15) and aliphatic compounds (10). (Buckingham, The Combined Chemical Dictionary, Chapman & Hall CRC, version 5:2, December 2001).
Phenolic compounds, particularly flavans are found in moderate to high concentrations in all Acacia species. (Abdulrazak et al. (2000) Journal of Animal Sciences. 13:935-940). Historically, most of the plants and extracts of the Acacia genus have been utilized as astringents to treat gastrointestinal disorders, diarrhea and indigestion and to stop bleeding. (Vautrin (1996) Universite Bourgogne (France) European abstract 58-01C: 177; Saleem et al. (1998) Hamdard Midicus. 41:63-67). The bark and pods of Acacia arabica Willd contain large quantities of tannins and have been utilized as astringents and expectorants. (Nadkarni (1996) India Materia Medica, Bombay Popular Prakashan, pp. 9-17). Diarylpropanol derivatives, isolated from stem bark of Acacia tortilis from Somalia, have been reported to have smooth muscle relaxing effects. (Hagos et al. (1987) Planta Medica. 53:27-31, 1987). It has also been reported that terpenoid saponins isolated from Acacia victoriae have an inhibitory effect on dimethylbenz(a)anthracene-induced murine skin carcinogenesis (Hanausek et al. (2000) Proceedings American Association for Cancer Research Annual Meeting 41:663) and induce apotosis (Haridas et al. (2000) Proceedings American Association for Cancer Research Annual Meeting. 41:600). Plant extracts from Acacia nilotica have been reported to have spasmogenic, vasoconstrictor and anti-hypertensive activity (Amos et al. (1999) Phytotherapy Research 13:683-685; Gilani et al. (1999) Phytotherapy Research. 13:665-669), and antiplatelet aggregatory activity (Shah et al. (1997) General Pharmacology. 29:251-255). Anti-inflammatory activity has been reported for A. nilotica. It was speculated that flavonoids, polysaccharides and organic acids were potential active components. (Dafallah and Al-Mustafa (1996) American Journal of Chinese Medicine. 24:263-269). To date, the only reported 5-lipoxygenase inhibitor isolated from Acacia is a monoterpenoidal carboxamide (Seikine et al. (1997) Chemical and Pharmaceutical Bulletin. 45:148-11).
Acacia gums have been formulated with other plant ingredients and used for ulcer prevention without identification of any of the active components. (Fuisz, U.S. Pat. No. 5,651,987). Acacia gums have also been formulated with other plant ingredients and used to improve drug dissolution (Blank, U.S. Pat. No. 4,946,684), by lowering the viscosity of nutritional compositions (Chancellor, U.S. Pat. No. 5,545,411).
The extract from the bark of Acacia has been patented in Japan for external use as a whitening agent (Abe, JP10025238), as a glucosyl transferase inhibitor for dental applications (Abe, JP07242555), as a protein synthesis inhibitor (Fukai, JP 07165598), as an active oxygen scavenging agent for external skin preparations (Honda, JP 07017847, Bindra U.S. Pat. No. 6,1266,950), and as a hyaluronidase inhibitor for oral consumption to prevent inflammation, pollinosis and cough (Ogura, JP 07010768).
Catechin is a flavan, found primarily in green tea, having the following structure.
Catechin works both alone and in conjunction with other flavonoids found in tea, and has both antiviral and antioxidant activity. Catechin has been shown to be effective in the treatment of viral hepatitis. It also appears to prevent oxidative damage to the heart, kidney, lungs and spleen. Catechin also has been shown to inhibit the growth of stomach cancer cells.
Catechin and its isomer epicatechin inhibit prostaglandin endoperoxide synthase with an IC50 value of 40 μmol/L. (Kalkbrenner et al. (1992) Pharmacol. 44:1-12). Five flavan-3-ol derivatives, including (+)-catechin and gallocatechin, isolated from four plant species: Atuna racemosa, Syzygium carynocarpum, Syzygium malaccense and Vantanea peruviana, exhibit equal to weaker inhibitory activity against COX-2, relative to COX-1, with IC50 values ranging from 3.3 μM to 138 μM (Noreen et al. (1998) Planta Med. 64:520-524). (+)-Catechin, isolated from the bark of Ceiba pentandra, inhibits COX-1 with an IC50 value of 80 μM (Noreen et al. (1998) J. Nat. Prod. 61:8-12). Commercially available pure (+)-catechin inhibits COX-1 with an IC50 value of around 183 to 279 μM depending upon the experimental conditions, with no selectivity for COX-2. (Noreen et al. (1998) J. Nat. Prod. 61:1-7).
Green tea catechin, when supplemented into the diets of Dawley male rats, lowered the activity level of platelet phospholipase A2 and significantly reduced platelet cyclooxygenase levels. (Yang et al. (1999) J. Nutr. Sci. Vitaminol. 45:337-346). Catechin and epicatechin reportedly weakly suppress COX-2 gene transcription in human colon cancer DLD-1 cells (IC50=415.3 μM). (Mutoh et al. (2000) Jpn. J. Cancer Res. 91:686-691). The neuroprotective ability of (+)-catechin from red wine results from the antioxidant properties of catechin, rather than inhibitory effects on intracellular enzymes, such as cyclooxygenase, lipoxygenase, or mitric oxide synthase (Bastianetto et al. (2000) Br. J. Pharmacol. 131:711-720). Catechin derivatives purified from green tea and black tea, such as epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and theaflavins showed inhibition of cyclooxygenase and lipoxygenase dependent metabolism of arachidonic acid in human colon mucosa and colon tumor tissues (Hong et al. (2001) Biochem. Pharmacol. 62:1175-1183) and induce COX-2 expression and PGE(2) production (Park et al. (2001) Biochem. Biophys. Res. Commun. 286:721-725). Epiafzelechin isolated from the aerial parts of Celastrus orbiculatus exhibited a dose-dependent inhibition of COX-1 activity with an IC50 value of 15 μM and also demonstrated anti-inflammatory activity against carrageenin-induced mouse paw edema following oral administration at a dosage of 100 mg/kg. (Min et al. (1999) Planta Med. 65:460-462).
Catechin and its derivatives from various plant sources, especially from green tea leaves, have been used in the treatment of HPV infected Condyloma acuminata (Cheng, U.S. Pat. No. 5,795,911) and in the treatment of hyperplasia caused by papilloma virus (Cheng, U.S. Pat. Nos. 5,968,973 and 6,197,808). Catechin and its derivatives have also been used topically to inhibit angiogenesis in mammalian tissue, such as skin cancer, psoriasis, spider veins or under eye circles (Anderson, U.S. Pat. No. 6,248,341), against UVB-induced tumorigenesis on mice (Agarwal et al. (1993) Photochem. Photobiol. 58:695-700), for inhibiting nitric oxide synthase at the level of gene expression and enzyme activity (Chan, U.S. Pat. No. 5,922,756), as a hair-growing agent (Takahashi, U.S. Pat. No. 6,126,940). Catechin based compositions have also been formulated with other extracts and vitamins for treatment of acne (Murad U.S. Pat. No. 5,962,517), hardening the tissue of digestive organs (Shi, U.S. Pat. No. 5,470,589), for inhibiting 5 alpha-reductase activity in treating androgenic disorder related diseases and cancers (Liao, U.S. Pat. No. 5,605,929). Green tea extract has been formulated with seven other plant extracts for reducing inflammation by inhibiting the COX-2 enzyme, without identification of any of the specific active components (Mewmark, U.S. Pat. No. 6,264,995).
To date, a number of naturally occurring flavonoids have been commercialized for varying uses. For example, liposome formulations of Scutellaria extracts have been utilized for skin care (U.S. Pat. Nos. 5,643,598; 5,443,983). Baicalin has been used for preventing cancer, due to its inhibitory effects on oncogenes (U.S. Pat. No. 6,290,995). Baicalin and other compounds have been used as antiviral, antibacterial and immunomodulating agents (U.S. Pat. No. 6,083,921) and as natural anti-oxidants (Poland Pub. No. 9,849,256). Chrysin has been used for its anxiety reducing properties (U.S. Pat. No. 5,756,538). Anti-inflammatory flavonoids are used for the control and treatment of anorectal and colonic diseases (U.S. Pat. No. 5,858,371), and inhibition of lipoxygenase (U.S. Pat. No. 6,217,875). These compounds are also formulated with glucosamine collagen and other ingredients for repair and maintenance of connective tissue (Bath, U.S. Pat. No. 6,333,304). Flavonoid esters constitute active ingredients for cosmetic compositions (U.S. Pat. No. 6,235,294). The bark, extract and compounds derived from Phellodendron amurense have been patented for use in treatment of inflammatory diseases (U.S. Pat. Nos. 5,766,614; 5,908,628; 6,113,909; 6,193,977). Cherry bioflavonoids from Prunus avium and Prunus cerasus with anthocyanidin type of structures have been patented as cyclooxygenase inhibitors (U.S. Pat. No. 6,194,469, U.S. Pat. Appl. 20010002407).